This invention relates to an improvement in the art of preparing tea extracts.
An ever increasing proportion of tea marketed in the world is marketed in the form of tea extracts, usually in the form of dry powders. Substantial research activity has been directed to the problems of obtaining tea extracts in the form of dry powders that upon reconstitution provide a high quality beverage, having a flavor and color which is as close as possible to that obtained by brewing tea from tea leaf. These processes may involve use of conditions which separately collect and set aside the flavor components before the tea is subjected to rigorous extraction conditions. The flavor components are then added back to the extracted water soluble tea solids at a subsequent stage in the process.
Another aspect of tea extract production is yield of soluble solids. For reasons of economics, processes which assure the highest possible recovery of water soluble solids from the tea leaf are desired.
Methods of obtaining tea extracts using a series of countercurrent stages are well-known in the art. The Bonotto U.S. Pat. No. 3,080,237, for example, discloses a process wherein fresh aqueous solvent is brought into contact first with the tea leaf which has been extracted in several earlier stages, and wherein the fresh dry tea leaf is first contacted with concentrated aqueous tea leaf extract. Temperatures of extraction varying from room temperature to elevated temperatures as high as 180.degree. C. or higher have been used, together with elevated pressures needed to maintain the high temperatures. The Mishkin et al. U.S. Pat. No. 3,451,823, for example, discloses a two-stage extraction wherein a first extraction stage is conducted at temperatures not exceeding 110.degree. C. to provide a first extract, the partially extracted leaf is comminuted and water added to form a pumpable slurry, and the slurry heated to 180.degree. C. to provide a second extraction. The two extracts are combined and dried to provide the product.
It is also known that strongly acid conditions at elevated temperature hydrolyze plant matter containing cellulose to saccharides. This is disclosed, for example, in the Jelks U.S. Pat. No. 3,939,286, where the process is used to treat cellulosic plant materials to increase the digestibility thereof by ruminants.